Germanium silicon oxynitride high index films for planar waveguides

ABSTRACT

A composition represented by the formula Si 1−x Ge x O 2(1−y) N 1.33y , wherein x is from about 0.05 to about 0.6 and y is from about 0.14 to about 0.74 exhibits properties highly suited for use in fabricating waveguides for liquid crystal based optical devices. In particular, the compositions have an index of refraction of from about 1.6 to about 1.8 for light at a wavelength of 1550 nm, and/or a coefficient of thermal expansion of from about 2.5×10 −6 ° C. −1  to about 5.0×10 −6 ° C.  −1 . The compositions also have inherently low hydrogen content, and a high hydrogen permeability which allows better hydrogen removal by thermal annealing to provide a material which exhibits low optical losses and better etching properties than alternative materials.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of U.S. application Ser. No.09/437,677 entitled GERMANIUM SILICON OXYNITRIDE HIGH INDEX FILMS FORPLANAR WAVEGUIDES, filed Nov. 10, 1999, the entire disclosure of whichis incorporated herein by reference.

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to materials for optical waveguides, andmore particularly to waveguide materials having a relatively high indexof refraction and/or a coefficient of thermal expansion which is nearlythe same as the coefficient of thermal expansion of silicon.

[0004] 2. Technical Background

[0005] Silicon oxynitride is a useful material for waveguides in planarphotonic devices, as well as for barrier layers and dielectrics indisplays and semiconductor devices. Silicon oxynitride is also ofinterest for use as a material for fabrication of photosensitive opticalfiber. By varying the nitrogen/oxygen ratio, films with a wide range ofrefractive indices and thermal expansions can be produced. Inparticular, silicon oxynitride films with a high nitrogen content are ofinterest for planar waveguides in optical devices utilizing liquidcrystals as an electro-optic material for total internal reflectance, inwhich a high refractive index (e.g., about 1.6 to about 1.8 for light ata wavelength of 1550 nm) planar waveguide is required.

[0006] Typically, silicon oxynitride is deposited by a chemical vapordeposition (CVD) technique, such as plasma enhanced chemical vapordeposition (PECVD) from the reaction of silane (SiH₄) and ammonia (NH₃).PECVD is favored for silicon oxynitride deposition because growth ratescan be as high as 15 micron/hour. However, the reaction of silane andammonia leads to the incorporation of large amounts of hydrogen (up to20% for Si₃N₄) in the films. This has several undesirable effects.First, the incorporation of large amounts of hydrogen in the filmsresults in high optical loss at 1550 nm. Another problem withincorporation of large amounts of hydrogen is that undesirablereduction-oxidation reactions occur between the hydrogen and surroundingmaterials. A further undesirable effect attributable to theincorporation of large amounts of hydrogen in a CVD deposited siliconoxynitride film is that such films cannot be as uniformly etched asfilms incorporating lower amounts of hydrogen.

[0007] When a large amount of hydrogen is present in a glass film formedby chemical vapor deposition, much of the hydrogen can usually beremoved with heat treatment techniques. However, hydrogen isparticularly difficult to thermally out-diffuse from a siliconoxynitride film formed by chemical vapor deposition because of the lowpermeability of hydrogen in the silicon oxynitride film. Unless carefuland time-consuming procedures are followed, the films tend to blisterand crack. The non-uniform dry-etching observed in high index siliconoxynitride films results from nanoscale (having a size of from about 1nm to about 1 micron) structures that contain both porosity that entrapshydrogen, and dense highly strained regions. Thermal annealing to removehydrogen, and relax and compact (densify) the glass film is required toachieve uniform etch rates and precisely defined etched structures.

[0008] Another disadvantage with silicon oxynitride films deposited byCVD results from the large thermal expansion mismatch between siliconand silicon oxynitride films having an appropriate nitrogen content forachieving the high refractive index required for liquid crystal opticaldevices. This thermal mismatch leads to high film strains which causebirefringence in waveguides, substrate curvature, and can cause filmcracking and/or delamination. Because of the disadvantages associatedwith incorporation of large amounts of hydrogen, and the large thermalexpansion mismatch between silicon and silicon oxynitride films, thefabrication of planar photonic devices using high index siliconoxynitride derived from the reaction of silane and ammonia does notappear to be commercially viable.

[0009] Therefore, it would be highly desirable if a high refractiveindex waveguide material having a coefficient of thermal expansion whichclosely matches the coefficient of thermal expansion of silicon could beprovided. It would also be highly desirable if a high refractive indexwaveguide material incorporating lower amounts of hydrogen and/or whichcould be more easily treated to remove incorporated hydrogen could beprovided. Even more desirable, would be a high refractive indexwaveguide material which has both a coefficient of thermal expansionwhich closely matches the coefficient of thermal expansion of silicon,and which incorporates a relatively lower amount of hydrogen duringchemical vapor deposition and/or allows easier removal of hydrogenincorporated during chemical vapor deposition.

SUMMARY OF THE INVENTION

[0010] The invention overcomes the problems inherent with high indexsilicon oxynitride films formed by chemical vapor deposition, andprovides a commercially viable method of fabricating a high refractiveindex waveguide material. More specifically, the invention provides agermanium silicon oxynitride material having an inherently lowerhydrogen content as deposited than silicon oxynitride; a higher hydrogenpermeability than silicon oxynitride, which facilitates hydrogenremoval; and a coefficient of thermal expansion which closely matchesthe coefficient of thermal expansion for silicon. These properties areextremely useful for fabricating optical devices based on total internalreflectance of liquid crystals.

[0011] In accordance with one aspect of the invention, a compositionrepresented by the formula Si_(1−x)Ge_(x)O_(2(1−y))N_(1.33y) is providedwherein x is from about 0.05 to about 0.6 and y is from about 0.14 toabout 0.74. Such compositions exhibit a relatively high index ofrefraction, and a coefficient of thermal expansion which closely matchesthe coefficient of thermal expansion for silicon.

[0012] In accordance with another aspect of the invention, the germaniumsilicon oxynitride composition has an index of refraction of from about1.6 to about 1.8 for light at a wavelength of 1550 nm.

[0013] In accordance with another aspect of the invention, the germaniumsilicon oxynitride composition has a coefficient of thermal expansion offrom about 2.5×10⁻⁶° C.⁻¹ to about 5.0×10⁻⁶° C.⁻¹.

[0014] In another aspect of the invention, a germanium siliconoxynitride film is deposited on a silicon substrate. The germaniumsilicon oxynitride film has an index of refraction of from about 1.6 toabout 1.8 for light at a wavelength of 1550 nm, and a coefficient ofthermal expansion of from about 2.5 ×10⁻⁶° C.⁻¹ to about 5.0×10⁻⁶° C.⁻¹.

[0015] In accordance with a further aspect of the invention, a germaniumsilicon oxynitride film deposited on a silicon substrate is representedby the formula Si_(1−x)Ge_(x)O_(2(1−y))N_(1.33y), wherein x is fromabout 0.05 to about 0.6 and y is from about 0.14 to about 0.74.

[0016] In accordance with another aspect of the invention, a process forforming a layer of glass having a relatively high index of refractionand a coefficient of thermal expansion which closely matches that ofsilicon is provided. The process includes the steps of providing asubstrate, and depositing on the substrate a layer of materialrepresented by the formula Si_(1−x)Ge _(x)O_(2(1−y))N_(1.33y), wherein xis from about 0.05 to about 0.6 and y is from about 0.14 to about 0.74.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a graph representing estimated refractive indicies at1550 nm for germanium silicon oxynitride compositions;

[0018]FIG. 2 is a graph representing estimated coefficients of thermalexpansion for germanium silicon oxynitride compositions;

[0019]FIG. 3 is a graph representing a region of primary interestdefined by the overlap of regions in FIGS. 1 and 2 which have an indexof refraction of from about 1.6 to about 1.8 at 1550 nm, and acoefficient of thermal expansion of from about 2.5×10⁻⁶° C.⁻¹ to about5.0×10⁻⁶° C.¹.

[0020]FIG. 4 is a graph of surface contours generated from a secondorder polynomial least squares fit of data for index of refraction at1550 nm for germanium silicon oxynitride as a function of filmcomposition;

[0021]FIG. 5 is a graph of surface contours generated from a secondorder polynomial least squares fit of data for hydrogen-nitrogen bondconcentration normalized to film thickness for germanium siliconoxynitride as a function of film composition;

[0022]FIG. 6 is a graph of surface contours generated from a secondorder polynomial least squares fit of data for stress as a function offilm composition; and

[0023]FIG. 7 is a schematic sectional view of a germanium siliconoxynitride film of the present invention deposited on a substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] The germanium silicon oxynitride compositions of this inventionare represented by the formula Si_(1−x)Ge_(x)O_(2(1−y))N_(1.33y),wherein x is from about 0.05 to about 0.6 and y is from about 0.14 toabout 0.74. Such compositions can be formed by chemical vapor depositionof germane (GeH₄), silane (SiH₄), nitrous oxide (N₂O) and ammonia (NH₃).The germanium silicon oxynitride glasses deposited by chemical vapordeposition in accordance with this invention have a relatively highindex of refraction, while exhibiting more favorable properties thansilicon oxynitride films having a comparable index of refraction. Morespecifically, the germanium silicon oxynitride glasses of this inventionhave a significantly lower hydrogen content when deposited than siliconoxynitride films having a comparable index of refraction. They also havea higher hydrogen permeability than silicon oxynitride having acomparable index of refraction, and a coefficient of thermal expansionwhich is more closely matched to the coefficient of thermal expansion ofsilicon. The inherently lower hydrogen content as deposited for thegermanium silicon oxynitride glasses results in lower optical losses at1550 nm than are exhibited by a comparable silicon oxynitride film, adecrease in undesirable reduction-oxidation reactions, and more uniformetching. The higher hydrogen permeability of the germanium siliconoxynitride glasses of this invention allows faster, easier and morethorough hydrogen removal by thermal annealing after deposition. Thecoefficient of thermal expansion of the germanium silicon oxynitrideglasses of this invention allow fabrication of high index waveguides onsilicon with reduced film strains, which reduces or eliminates thepossibility of strain-induced birefringence in optical waveguides. Also,by more closely matching the refractive index of the deposited germaniumsilicon oxynitride glasses to the coefficient of thermal expansion of asilicon substrate, the reduction in film strains also leads to reducedsubstrate curvature, whereby the possibility of film cracking ordelamination is eliminated, or at least very substantially reduced.

[0025] Properties, such as refractive index, of germanium siliconoxynitride as a function of composition are represented graphically asshown in FIG. 1, wherein the abscissa represents the ratio of germaniumto germanium plus silicon (i.e., Ge/(Si+Ge)), and the ordinaterepresents the ratio of nitrogen to nitrogen plus oxygen (i.e.,N/(N+O)). The lower left hand comer of the graph (FIG. 1) representspure silica (SiO₂), the lower right hand comer represents pure germania(GeO₂), the upper left hand comer represents pure silicon nitride(Si₃N₄), and the upper right hand corner represents pure germaniumnitride (Ge₃N₄). Properties for the compounds represented at the comersof the graph, SiO₂, GeO₂, Si₃N₄ and Ge₃N₄, are listed in Table 1. TABLE1 Refractive index and thermal expansion data for GeSiON end members.Density n(632) n(1550) α*10⁷ ° C.⁻¹ (g/cc) SiO₂ 1.4578 1.444 7 2.63 GeO₂1.650 1.587 64 4.228 Si₃N₄ 1.95 1.91 30 3.1 Ge₃N₄ 2.23 2.14 ? 5.25

[0026] The surface contour lines shown in FIG. 1 represent estimatedrefractive index at 1550 nm for germanium silicon oxynitridecompositions based on the properties of SiO₂, GeO₂, Si₃N₄ and Ge₃N₄. InFIG. 2, the surface contour lines represent estimates of thermalexpansion for germanium silicon oxynitride compositions. The valuesindicated in Table 2 and FIG. 2 are expressed in linear units ofexpansion per ten million linear units per ° C. (e.g., in/10⁷in/° C.).

[0027] For optical devices based on total internal reflectance of liquidcrystals, a refractive index of from about 1.6 to about 1.8 at thewavelength of interest (typically about 1550 nm) is required. Forsilicon oxynitride, this refractive index range is achieved byincreasing the nitrogen content of the glass. However, increasingnitrogen content also increases hydrogen content. By substitutinggermanium for silicon, the refractive index of the glass may beincreased while incorporating substantially less hydrogen. From FIG. 1,it can be seen that an index of refraction in the range of from about1.6 to about 1.8 can be achieved over a large diagonal range ofcompositions starting from mostly silicon nitride rich glass to mostlygermanium oxide rich glass. The thermal expansion of this range variesfrom about 1.5 to about 2.5 ppm per ° C. (15×10⁻⁷° C.⁻¹ to 25×10⁻⁷°C.⁻¹) for the silicon glass that is mostly nitride, and from about 6.0to about 7.0 ppm per ° C. (60×10−7° C.⁻¹ to 70×10⁻⁷° C.⁻¹) for agermanium glass that is mostly oxide. By overlapping a composition rangein which the coefficient of thermal expansion is closely matched to thecoefficient of thermal expansion for silicon (about 3.7 ppm per ° C.)with a composition range having the desired refractive index range,estimates of the compositions of most interest for optical devices basedon total internal reflectance of liquid crystals may be derived, asshown in FIG. 3. The region of primary interest is estimated to becentered at a Ge/(Ge+Si) ratio of about 0.3 and a N/(N+)) ratio of about0.4. More specifically, the region R of interest shown in FIG. 3approximately encompasses those compositions of germanium siliconoxynitride having an index of refraction at 1550 nm of from about 1.6 toabout 1.8, and a coefficient of thermal expansion of from about2.5×10⁻⁶° C.⁻¹ to about 5.0×10⁻⁶° C.⁻¹ (i.e., from about 2.5 ppm per °C. to about 5.0 ppm per ° C.).

[0028] Planar waveguiding films appropriate for optical devices may bedeposited by numerous techniques including physical vapor deposition(PVD) processes including sputtering, electron beam evaporation,molecular beam epitaxy, and laser ablation, or by chemical vapordeposition (CVD) processes including flame hydrolysis deposition (FHD),atmospheric pressure chemical vapor deposition (APCVD), low pressurechemical vapor deposition (LPCVD), plasma enhanced chemical vapordeposition (PECVD), and chemical beam epitaxy. For typical planaroptical devices having an index of refraction which is matched to theindex of refraction of an optical fiber, flame hydrolysis deposition(FHD) and PECVD have been the most widely utilized methods because oflow waveguiding propagation losses and excellent compositional andthickness uniformity. The germanium silicon oxynitride films of thisinvention may be applied using generally any of the physical vapordeposition processes or any of the chemical vapor deposition processes,with preferred deposition processes including PECVD and LPCVD.

[0029] In accordance with an aspect of this invention, a planar opticaldevice is prepared from a precursor article 10 (FIG. 7) comprising agermanium silicon oxynitride film 12 deposited on a silicon substrate14. The germanium silicon oxynitride film 12 has an index of refractionof from about 1.6 to about 1.8 for light at a wavelength of 1550 nm, anda coefficient of thermal expansion of from about 2.5×10⁻⁶° C.⁻¹ to about5.0×10⁻⁶° C.¹. Germanium silicon oxynitride film 12 deposited on siliconsubstrate 14 using a CVD or PVD deposition process is represented by theformula Si_(1−x)Ge_(x)O_(2(1−y))N_(1.33y), wherein x is from about 0.05to about 0.6 and y is from about 0.14 to about 0.74.

[0030] After the germanium silicon oxynitride film has been deposited,it is preferably thermally annealed to remove hydrogen. Effectiveannealing temperature range from about 600° C. to about 1000° C., withsuitable annealing times ranging from about 3 minutes to about 1000minutes. The annealing process is preferably conducted at a partialpressure of oxygen which is very low, preferably less than about10^(×30) atmospheres.

EXAMPLES

[0031] CHEMICAL VAPOR DEPOSITION

[0032] A plasma enhanced chemical vapor deposition process was used fordeposition of germanium silicon oxynitride films having propertiesappropriate for optical devices based on total internal reflectance ofliquid crystals. These films were deposited by PECVD using a parallelplate reactor with a heated stationary platten, a low frequency (375kHz) RF generator and matching network, and a gas manifold supplyingsilane, germane, nitrous oxide, ammonia, and nitrogen into the processchamber through a showerhead nozzle uniformly distributes the reactivegases. The process conditions for the samples are in Table 2. TABLE 2Process conditions for PECVD GeSiON films Glass Flow rate (sccm)Temperature Pressure Deposition sample 5% SiH4 2% GeH4 N2O NH3 RF (w)Substrate Showerhead (mtorr) Time (min) 1 400 0 2000 0 400 300 200 55040 2 400 0 50 300 400 350 225 500 40 3 300 125 50 300 400 350 225 500 404 350 63 50 300 400 350 225 500 40 5 200 250 50 300 400 350 225 500 40 6350 63 70 200 400 350 225 500 40 7 200 250 70 200 400 350 225 500 40 8350 63 200 200 400 350 225 500 40 9 200 250 200 200 400 350 225 500 4010 0 500 200 200 400 350 225 500 40 11 400 0 0 300 400 350 225 500 40 120 500 0 300 400 350 225 500 40

[0033] Film surface morphology was examined by scanning electronmicroscopy (SEM) and atomic force microscopy (AFM). The thickness andreactive index of each of the films was determined by a prism couplingsystem. The composition was determined by electron microprobe, and thehydrogen concentration was determined by both Fourier Transform infraredSpectroscopy (FTIR) and proton solid state nuclear magnetic resonance(¹H-SSNMR). Compositions of the germanium silicon oxynitride films weremapped to an idealized hydrogen free compound represented by the formulaSi_(1−x)Ge_(x)O_(2(l−y))N_(1.33y). Film stress was determined frommeasurements of wafer curvature using Stoney's equation. See MiltonOhring, The Materials Science Of Thin Films, Academic Press, on (1992),pp. 416-420. Some error in stress measurements is expected because thecurvature of the substrates was not measured prior to deposition. Theresults of microprobe, prism coupling, FTIR, and wafer curvaturemeasurements are listed in Table 3. TABLE 3 Composition and propertiesof PECVD GeSiON Films Compositional Map WT. % ELEMENTSi(1−x)GexO2(1−y)N4/3*y Growth Stress sample Si Ge N O x y n(632)n(1550) (micron/hr) [NH1/t (Mpa) 1 — — — — 0 0 1.4571 1.4439 14.072 0 250.855 0.001 33.831 11.659 0.000 0.768 1.7663 1.7413 8.63 0.0739 −860.13 39.096 19.819 29.976 9.526 0.164 0.782 1.8131 1.7837 7.50 0.0828 −29884 45.631 9.083 31.707 11.027 0.072 0.767 1.7788 1.7517 8.35 0.0762 82.355 27.253 37.354 24.899 7.860 0.347 0.783 1.8815 1.8460 6.70 0.0732 −73506 45.010 8.910 28.036 14.761 0.071 0.684 1.7420 1.7168 9.05 0.0744 651.37 28.488 35.268 21.820 12.045 0.324 0.674 1.8221 1.7887 7.85 0.0740207.4 8 43.891 8.474 22.481 22.659 0.070 0.531 1.6736 1.6513 9.71 0.06551396 9 27.906 34.169 16.829 19.462 0.321 0.497 1.7343 1.7059 8.49 0.0619971.1 10 0.771 69.398 6.634 21.468 0.972 0.261 1.7315 1.7037 7.57 0.049511 58.639 0.002 35.220 0.197 0.000 0.995 1.9514 1.9132 11.6406 0.0481 120.719 76.528 17.535 1.952 0.976 0.911 2.2294 2.1446 3.6092 0.1535

[0034] SEM micrographs of the surface and cross section of film Sample9, and an AFM image of a region of the surface of film Sample 9 wereevaluated to determine that the were smooth and uniform as deposited.X-ray diffraction was used to determine that the films were amorphous asdeposited. The quantity of hydrogen-nitrogen bonds normalized tothickness was determined using FTIR, and the results are listed in Table3 under the heading “[NH]/t”.

[0035] A first and second order polynomial least squares fit wasperformed on the data listed in Table 3 to relate the film compositionto the index of refraction at 632 nm, the of refraction at 1550 nm, thegrowth rate in microns per hour, the relative concentration ofnitrogen-hydrogen bonds normalized to thickness, and the stress in MPa.The results of the polynomial least squares fits are shown in Table 4,and the resulting surface contours for refractive index at 1550 nm,relative nitrogen-hydrogen bond content, and film stress are illustratedin FIGS. 4, 5 and 6, respectively. The regions of the graphs shown inFIGS. 4, 5 and 6 which indicate compositions which produce desirablerefractive stress and hydrogen content coincide very closely with theregion R of interest shown in FIG. 3. TABLE 4 First and second ordercoefficients for least squares fit of film properties to compositionGrowth n(632) n(1550) Rate [NH1/t Stress First order coefficients ax0.2875 0.2533 −5.4486 0.0522 −11235 by2 0.5328 0.4957 −5.4086 0.0880−18449 m 1.3792 1.3798 13.6070 −0.0011 13588 Variance 0.0025 0.00171.9334 0.0004 3823343 Second order coefficients ax2 0.0056 −0.0128−0.10941 0.0991 −43477 by2 0.2897 0.26782 13.6750 −0.1920 −155140 cxy0.2359 0.1743 −4.8525 0.1442 −82553 dx 0.1461 0.1664 −2.2165 −0.134863415 ey 0.1820 0.1824 −17.7390 0.2445 198920 m 1.4617 1.4479 14.8880−0.0009 −62017 Variance 0.0004 0.0003 0.6445 0.0000 1530399

[0036] ANNEALING

[0037] PECVD deposited germanium silicon oxynitride films were annealedby two processes. Initially, films were annealed in a muffle furnace inair by bringing the furnace to a desired temperature and quicklyinserting the sample into the hot furnace. The sample was then removedfrom the hot furnace when the desired time had elapsed. Table 5 liststhe results of annealing films of Sample 9 by this process. Annealingexperiments at temperatures up to 700° C. for 830 minutes resulted in a20% reduction in the relative concentration of hydrogen-nitrogen bondsnormalized to thickness. However, this reduction in hydrogen content wasaccompanied by a 1.2% decrease in the index of refraction, and a 1.5%decrease in thickness. This is believed to result from oxidation of thefilm, and perhaps volatilization of SiO and GeO. An Ellingham diagram(not shown) calculated from the oxidation of silicon nitride into silicaindicated that for annealing at 1000° C, a partial pressure of oxygenless than 10⁻³⁰ atmospheres is desired to prevent oxidation. TABLE 5Annealing of T041699B GeSiON in air Temp (C) Time (min) n(632) n(1550)thickness [NH1/thick 0 0 1.7251 1.6978 5.8105 0.0609 600 23 1.71661.6901 5.7181 0.0635 600 285 1.7133 1.6862 5.7184 0.0610 600 960 1.71231.6868 5.7241 0.0599 700 960 1.7015 1.6772 5.6926 0.0511 725 990 1.70591.6805 5.7225 0.0458 750 990 1.7114 1.6851 5.6596 0.0353 800 3 1.71131.6877 5.7304 0.0534 650 830 1.7078 1.6829 5.7638 0.0545 700 830 1.70371.6793 5.7267 0.0496

[0038] Germanium silicon oxynitride films were also annealed in vacuumusing a pyrolytic boron nitride substrate heater in a small stainlesssteel chamber evacuated by a dual stage rotary pump to a pressure ofabout 50 mtorr. Table 6 lists the results of annealing films of Sample 9by this process. Vacuum annealing of germanium silicon oxynitride filmswas shown to be highly effective in removal of hydrogen incorporatedduring deposition. FTIR indicates that vacuum annealing for 30 minutesat 750° C. removed 85% of the incorporated hydrogen bonded to nitrogen,and solid state NMR shows all detectable hydrogen (both N—H and Si—H)was removed. TABLE 6 Annealing of T041699B GeSiON in vacuum Temp (C)Time (min) n(632) n(1550) Thickness [NH1/thick 0 0 1.7251 1.6978 5.81050.0609 750 30 1.7566 5.9594 0.0112

[0039] The compositions of germanium silicon oxynitride of thisinvention are appropriate for fabrication of waveguides for liquidcrystal planar optical devices. The only competitive material andprocess for deposition of high refractive index (from about 1.6 to about1.8) waveguides for liquid crystal based optical devices for whichequipment is commonly available is PECVD deposited silicon oxynitride.Compared to silicon oxynitride, the PECVD deposited germanium siliconoxynitride glasses of this invention have significantly lower hydrogencontent as deposited, and higher hydrogen permeability which enablesbetter hydrogen removal by thermal annealing. Further, the germaniumsilicon oxynitride glasses of this invention can be nearly expansionmatched to silicon, which allows fabrication of high index waveguides onsilicon. These properties make these films highly appropriate foroptical devices based on total internal reflectance of liquid crystals.

[0040] It will become apparent to those skilled in the art that variousmodifications to the preferred embodiment of the invention as describedherein can be made without departing from the spirit or scope of theinvention as defined by the appended claims.

What is claimed is:
 1. An optical waveguide including a core comprisinga composition represented by the formulaSi_(1−x)Ge_(x)O_(2(1−y))N_(1.33y), wherein x is from about 0.05 to about0.6 and y is from about 0.14 to about 0.74.
 2. The optical waveguide ofclaim 1, wherein the core has an index of refraction of from about 1.6to about 1.8 for light at a wavelength of 1550 nm.
 3. The opticalwaveguide of claim 1, wherein the composition has a coefficient ofthermal expansion of from about 2.5×10⁻⁶° C.⁻¹ to about 5.0×10⁻⁶° C.⁻¹.4. The optical waveguide of claim 2, wherein the composition has acoefficient of thermal expansion of from about 2.5×10⁻⁶° C.⁻¹ to about5.0×10⁻⁶° C.⁻¹.
 5. An optical waveguide including a core comprising acomposition of germanium silicon oxynitride having an index ofrefraction of from about 1.6 to about 1.8 for light at a wavelength of1550 nm.
 6. The optical waveguide of claims 5, wherein the core has acoefficient of thermal expansion of from about 2.5×10⁻⁶° C.⁻¹ to about5.0×10⁻⁶° C.⁻¹.